1. Technical Field
The present invention generally relates to a sensor or gage; and more particularly to a sensor or gage for arranging in a bearing frame or housing of a pump forming part of a pumping system.
2. Description of Related Problem There are several commonly employed methods for determining the fluid level, e.g. oil, in bearing frame housing of rotating equipment:
For example, a sight glass oil level gauge may be screwed into the bearing housing in such a way that the center of the gage is located at the desired oil level. The gage uses a transparent glass or plastic window 6 to view the oil level. FIG. 8 shows, by way of example, one such known gage generally indicated as 5. The correct oil level is achieved when the level of oil seen through the transparent window 6 coincides with a level mark built into the gage. The sight glass oil level gage may employ a small baffle with a hole 7, stamped or drilled in the center. However, the disadvantage of the sight glass oil level is that it requires a person to visually check the oil level. The level must be checked at regular intervals.
Capacitive sensors may determine the oil level by measuring the capacitance between plates or coils immersed in the oil. The presence of oil between the sensor plates or electrodes is reflected in a change in capacitance. The capacitance is determined by some type of electronic device that equates the capacitance to the oil level. Moreover, inductive or capacitive sensors are known that are typically screwed into the bottom of the bearing housing. The sensor's length is such that it protrudes through the oil. The oil level is inferred by measuring the inductance or capacitance of the sensor. This type of sensor can be used to automatically annunciate alarms or warnings on low or high oil level, when attached to a personal computer (PC), a supervisory control or data acquisition (SCADA) system or a distributed control system (DCS). The inductive or capacitive sensors must be available in many lengths to accommodate all of the different bearing house designs. To determine the oil level or change in oil level, a reference capacitance must be taken for each housing design. Most times this type of sensor is screwed into the oil drain hole plug connection, which necessitates removing wire, etc. when draining the oil. Otherwise, an extra plug connection on the bottom of the housing is required. The disadvantage of the capacitive sensors is that it may or may not give a correct indication of oil level depending on the presence of contamination in the oil and the correct calibration and set-up of the sensor. There is no way to verify that the level is correct. The oil level is determined by measuring capacitance between plates or probes immersed in the oil. The capacitance is determined in part by the dielectric properties of the oil and air. Unfortunately, the difference between the dielectric constant of oil versus air is small. Air has a dielectric constant of 1 and common mineral oils have a dielectric constant of 2. Water has a dielectric constant ranging from 48 to 88. If the oil is contaminated with even small amounts of water the dielectric properties are drastically altered making oil level measurements inaccurate or suspect at best.
A level plug may be located horizontally in the bearing housing so that the bottom of the threaded hole is at the desired oil level. The level is checked by removing the plug. If oil flows out, the level is too high. If the oil is seen at the bottom threads, then the oil level is correct; and if oil is not seen, then the oil level is low. This method is commonly used on transmissions and gear boxes. However, the disadvantage of the level plug is that it requires a person to physically remove a plug with some type of tool and visually check for the presence of oil. Removing the plug exposes the oil to liquid or solid contaminants that may be around the plug.
Dip sticks are also commonly used on internal combustion engines to determine the correct oil level. The stick which has marks or lines or holes placed at the desired oil level on the stick. Removing the dip stick from the dip tube and observing the location of the residual oil in relation to the markings on the stick gives an indication of the oil level. However, the disadvantage of using a dip stick to monitor oil level is that it requires a person to physically remove the stick, wipe off the oil, reinsert the stick, remove the stick and match the wetted oil line with the marking on the stick. This also exposes the oil to contamination from the surroundings.
Other known level sensing techniques include that disclosed in U.S. Pat. No. 4,152,937, which provides for a liquid level sensor having a level mutual inductance probe with primary and secondary windings wound coextensively inside a closed end tubular protective housing; as well as that disclosed in U.S. Pat. No. 6,520,011, which provides for a powder detecting capacitive type sensor having a sensor body having a pair of electrodes inside and a circuit that detects a change of capacitance between the electrodes so as to detect the existence of powder adjacent the sensor body, where the sensor is arranged on a wall of a powder tank.